Collision-Induced Molecular Absorption in Stellar Atmospheres

Abstract

Collision-induced absorption (CIA) arises in small complexes of inert atoms or molecules due to dipole moments temporarily induced during intermolecular interactions. It is well known that CIA is the major source of the infrared opacity of dense planetary atmospheres, which are composed of nonpolar molecules. However, CIA also plays a significant role in the opacity of cool stars(having low free electron densities) composed of hydrogen and helium gas. Model atmospheres of the cool, high-gravity stars, such as white dwarfs, M (red) dwarfs, brown dwarfs, and the (hypothetical) “population III” stars show that at low enough temperatures and/or at high enough densities CIA may be the dominant source of opacity in the infrared region below 15,000 cm-1. A review is given of all types of stars whose atmospheric opacity may be strongly affected by CIA. Moreover, existing needs, related to CIA and model atmospheres, are indicated.